Impact of fertilization on a salt marsh food web in Georgia

I examined the response of a salt marsh food web to nutrients, and spatial variation in this response, at 19 sites on the Georgia coast. In fertilized treatments, Spartina alterniflora increased at the expense of Juncus roemerianus. Spartina dominance was reduced at sites with greater upland influence, regardless of fertilization. Because fertilization changes plant quantity and quality, it could also affect consumers of plants. Fertilization positively influenced herbivores (grasshoppers), had little effect on decomposers (fungi), and no effect on detritivores (snails). The two snail species Littoraria irrorata and Melampus bidentatus were negatively correlated with each other and likely compete. Natural variation among sites was typically similar or greater than impacts of fertilization. These results suggest that eutrophication of salt marshes is likely to have stronger impacts on plants and herbivores than on decomposers and detritivores, and that impacts are not likely to be much greater than variation among sites.